drm/amdgpu: add inst to amdgpu_dpm_enable_vcn

Add an instance parameter to amdgpu_dpm_enable_vcn() function, and change
all calls from vcn ip functions to add instance argument. vcn generations
with only one instance (v1.0, v2.0) always use 0 as instance number. vcn
generations with multiple instances (v2.5, v3.0, v4.0, v4.0.3, v4.0.5,
v5.0.0) use the actual instance number.

v2: remove for-loop in amdgpu_dpm_enable_vcn(), and temporarily move it
to vcn ip with multiple instances, in order to keep the exact same logic
as before, until further separation in next patch.

v3: fix missing prefix

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>